Foundry processes and metallurgical addition agents therefor

ABSTRACT

The invention relates to metal melting processes, particularly electroslag remelting processes, in which a metallurgical addition agent in the form of coated aluminium-containing particles is used. The coating is at least one of the metals selected from the group consisting of nickel, cobalt and iron. A preferred metallurgical addition agent is disclosed which consists of particles of an aluminium-lithium alloy having a coating of at least one metal selected from the group consisting of nickel, cobalt and iron.

United States Patent [1 1 Fontaine et al.

FOUNDRY PROCESSES AND METALLURGICAL ADDITION AGENTS THEREFOR Inventors: Paul Isidore Fontaine, Solihull,

England; Louis Favillier, Brussels, Belgium Assignee: The International Nickel Company,

Inc., New York, N.Y.

Filed: Sept. 3, 1974 Appl. No.: 502,625

Foreign Application Priority Data Sept. 7, 1973 United Kingdom 42221/73 US. Cl 75/10 R; 75/53; 75/58; 75/93 G; 29/1962 Int. Cl. C223 4/00; C21C 7/00; C2213 9/12;

Field of Search 75/10, 53, 58, 93 G, 129, 75/130, 130.5, .5 AA, .5 BA; 29/1962,

Primary Examiner-Peter D. Rosenberg Attorney, Agent, or Firm-George N. Ziegler; Ewan C. MacQueen; Raymond J. Kenny [57 ABSTRACT The invention relates to metal melting processes, particularly electroslag remelting processes, in which a metallurgical addition agent in the form of coated aluminium-containing particles is used. The coating is at least one of the metals selected from the group consisting of nickel, cobalt and iron. A preferred metallurgical addition agent is disclosed which consists of particles of an aluminium-lithium alloy having a coating of at least one metal selected from the group consisting of nickel, cobalt and iron.

17 Claims, N0 Drawings FOUNDRY PROCESSES AND METALLURGICAL ADDITION AGENTS THEREFOR The present invention relates to metallurgical addition agents suitable as foundry additives, and in particular as additives for electroslag remelting processes, and to processes wherein said agents are used.

In electroslag remelting of metals a fusible electrode of the metal is fed continuously into a pool of slag which covers a pool of metal contained in a cooled mould, and the electrode is melted and the slag is maintained molten by the passage of an electric current through the slag between the electrode and the pool of molten metal. The process is sometimes also known as electroflux remelting.

The fusible electrode may be a solid bar, rod or wire and alloying additions may be continuously fed into the slag pool in the form of metallic powder or granules. The electrode may also be a tube or strip containing a core of metallic powder which is melted and alloys with the metal of the tube or strip.

Moreover in recent modifications of this process, for example as described in Canadian patent specification No. 849,107 and British specification No. 1,089,456 known as continuous electroslag powder remelting process (CESPM), rod or strip electrodes are employed which are surrounded by magnetically or mechanically held powders and which are mixed to produce a resultant ingot of the desired composition.

In general foundry practice, including the production of metals and alloys by electroslag remelting, small additions of elements and master alloys are frequently made in order to improve the physical and chemical characteristics of the resultant ingot. For example aluminium, calcium and magnesium are used as deoxidants, and magnesium is also used in the production of spheroidal graphite. In electroslag remelting, finelydivided aluminium, generally as powder or tumings is added with other powder additions to the slag pool. Although the aluminium is effective as a deoxidiser, substantial losses occur since the aluminium tends to float on the surface of the slag pool, where part of it reacts with oxygen in the atmosphere. Some of the aluminium also reacts with oxygen dissolved in the slag pool. The aluminium oxide formed by these reactions tends to enter the metal as a fine dispersion, where it shows up as part of the total oxygen content of the solidified metal.

It has been proposed that lithium should be used as a foundry additive to reduce the hydrogen content of the resultant ingot, but in practice the extreme reactivity of lithium with air and on addition to the melt, together with its low density, causing very low recovery, pre elude its use despite the desirability of reducing the hydrogen content of ingots.

US. patent 1,922,037 proposes that alkali metals be agglomerated or briquetted but specifically not alloyed with other metals in order to moderate their reactivity and put them into a form suitable for use as metallurgical additives. This does not appear to have become a common practice.

It is an object of the present invention to provide a metallurgical additive for foundry use which is particularly suitable for the introduction of aluminium into the slag pool of an electroslag remelting process.

It is a further object of the invention to provide a lithium-containing metallurgical additive for foundry use.

According to the present invention a metal melting process is provided wherein a metallurgical addition agent is added to the melt in the form of coated aluminium-containing particles, the coating of which comprise at least one of the metals selected from the group consisting of nickel, cobalt and iron.

in accordance with one aspect of the invention, an electroslag remelting process is provided wherein a metallurgical addition agent is added to the slag pool in the form of coated aluminium containing particles, the coating comprising at least one of the metals selected from the group consisting of nickel, cobalt and iron.

The use of coated particles in electroslag remelting has three main advantages: first, the coating prevents reaction between the aluminium and the air before it enters the slag, and second, the higher density of the coated particles make them sink into the slag pool and the molten metal, so that the aluminium reacts only with oxygen and lower order oxides in the molten metal or in the slag. Thus the efficiency of the process is increased, since less aluminium is consumed by reaction with oxygen in the air and deoxidation is effected by means of a smaller addition of aluminium, and furthermore the total oxygen content of the solidified metal is substantially lowered, as it contains less entrapped aluminium oxide. The third advantage is that the coating renders the particles magnetic, so that the powder can be caused to adhere to the electrode by the magnetic field resulting from the passage of electric current. There may also be a significant reduction in the nonmetallic inclusion content of the resultant alloy.

Metallurgical addition agents used in processes of the present invention may consist of coated aluminium powder or of coated particles of an aluminium-based alloy. Other constituents of the aluminium-based alloy should not, of course, be detrimental to the resultant ingot, and may advantageously be other metals commonly used for the treatment of the metals and alloys being melted, for example calcium, lithium or magnesium. Preferably in excess of 20% by weight of the metallurgical addition agent comprises nickel.

According to a further aspect of the present invention, a metallurgical addition agent for foundry use comprises particles of an aluminium-lithium alloy having a coating of at least one of the metals selected from the group consisting of nickel, cobalt and iron. Preferably the particles are of an alloy of composition 5 to 45% lithium by weight, balance aluminium and impurities.

A preferred metallurgical addition agent of the invention comprises particles of an alloy of composition 16 24% lithium by weight, balance aluminium and impurities and having a coating of at least one of the metals selected from the group consisting of nickel, cobalt and iron. The composition of this alloy is based on a known lithium-aluminium interrnetallic compound.

It has been found that the use of the preferred metallurgical addition agent consisting of coated particles of lithium-aluminium alloy in foundry practice, including electroslag remelting, may lead to a significant reduction in the hydrogen content, and the non-metallic inclusion content of the resultant ingot. Moreover the shelf life of the additive is high, providing good encapsulation has been achieved, the density of the particles is greater than the comparative uncoated particles so that the particles are more inclined to sink into the melt rather than float. leading to higher efficiency. Furthermore the oxygen and sulphur contents of the resultant ingot may be reduced.

The preferred metallurgical addition agent is particutrode composition of 5l% nickel, balance iron, and using a calcium fluoride, calcium oxide, alumina based slag. The process was operated, nominally at 32V, 2000A, with a variety of deoxidants and the oxygen larly useful in the production of ingot of alloy steels, 5 contents of the resultant ingots determined. The results nickel-iron and nickel-chromium-iron alloys and of are set out in Table l. other base materials. TABLE I The metal coatings on the metallurgical addition agents for use in the production of ingot according to Demoldams Fem N 'l k Content lRClUSlOflS the present invention may be produced by any conves 1 I '7 nient coating process. It has been found that a particu- A Aluminium powder 3 3;; Significant larly convenient way of producing a nickel coating by 025, Al Aluminium Powder 0016 improved the thermal decomposition of nickel carbonyl, advantageously while the aluminium powder or aluminium 0227676 M 83% Ni Nicoaled 0mg i 'j lgj based alloy particles are maintained in the form of a 15 Al powder fluidised bed. Iron coatings may also be conveniently g gz l g i -gz g as Sample 2 produced in this way, and complete encapsulation of Mg no particles with nickel and/or iron is readily achieved. AH 513% M Ni-wated 0-010 y low Other techniques which may be used to provide the 007% Ca fil fi ffjgg g coated particles may include wet processes, except in the production of coated aluminium-lithium alloy or calcium containing particles, and sputtering (vacuum deposition) techniques. EXAMPLE u Generally, suitable particle sizes for the coated parti- A ll f 20% li hi b l l i i was eles is in range to 2mm, and Preferably to pared, and was comminuted to form aluminium-lithium ljmrh- If the Particles are Small y tend be alloy particles. These were coated by the decomposiblewh the eohveeheh currents, Particularly above tion of nickel carbonyl so that about 61% of the total the slag pool of an electroslag remelting process, while i h f h Coated id was i k L the PartieleS Should be 50 large y do net Continuous additions of the coated particles were meh q y enough or de not react Completely with made to the slag pool of an electroslag remelting prolhe "when melfllcess using a 9% nickel steel electrode having a hydro- Metallurgical addition products may be added in progen Qomem f 10 ppm d an Oxygen content f cesses of the present invention in any convenient way, 0 015% A calcium fl rid calcium id l i either Separately or admixed other additives, Such based lag was used The remelting process was opcratas metal powders, desirable elemental additions, eg i i ll at 32V 2000A t produce a |5() di- Ca, Mg, and coated particles of calcium and/or magneamder ingot sium in which the coating is at least one of the metals F comparison, ddi i of 50% Ni NL d nicke C(J a ifOnminium powder were made in an identical electroslag PaYhehiarlY advahtageohs results are Obtained lh P remelting process. The results are set out in Table II. cesses of the present invention in which the metallurgi- TABLE II cal addition agent is admixed with premixed metal powders of a desired composition and are used to suri e Oxygen Hydrogen PP round a rod or strip electrode in a CESPM process as 015 A] described and claimed in UK. patent 1,089,456. Ni-coated A1 0H w 4 Examples of ferrous alloys that may advantageously giiggkfif' 0013 20 be deoxidised during electroslag remelting by means of nickel, cobaltor iron-coated aluminium-containing particles are alloy steels, nickel-iron and nickelchromium-iron alloys. The metal of the coating may be EXAMPLE Selected having regard to the Composition of the alloy Similar tests to those of Example I] were carried out being producedusing a 51% Ni: 49% Fe electrode having an initial hy- Some examples of the processes in accordance with dmgen content f 20 ppm and Oxygen content f the invention will now be described by way of example 001 5%. ohly- Analyses were made for oxygen, hydrogen and sul- EXAMPLE 1 55 phur content of the top central region and the body of the ingot obtained in each case. The results are set out A series of 150mm. diameter ingots was prepared by in Table n a typical electroslag remelting process from an elec- TABLE 1]] Sample Additive Form Oxygen Hydrogen Sulphur 1: pp

content content content 1 Top central .17 Al Ni coated- .(]l l l8 2l .004 Body Al powder .()ll 13 I4 .002 ll Top central .153 AH Ni coated- DH 16 i7 .003 Body .038 Li Al-Li alloy .009 ms I4 .003 Ill Top central .l AH Ni coated ,009 l(].5 002 TABLE Ill-continued Sample Additive Form Oxygen Hydrogen Sulphur 7c content cri ri t nt content Body .049 Li Al-Li alloy .007 7.5 s .002

sisting of aluminium-calcium, aluminium-magnesium EXAMPLE W [0 and aluminium-lithium alloys.

in a continuous electrode powder remelting process (CESPM) a mild steel electrode was used together with metal powder in proportions to give an ingot of composition 25% Cr, 12% Ni, balance Fe. When 0.1 to 0.2% aluminium powder was used as deoxidant the oxygen content of the resultant ingot was found to be 139 ppm. When a similar percentage of aluminium in the form of nickel coated aluminium powder was used however the oxygen content of the resultant ingot was 90 ppm. A very significant reduction in the non-metallic inclusion content of the ingot was also found in the latter case.

Although the present invention has been described in conjunction with preferred embodiments, it is to be understood that modifications and variations may be resorted to without departing from the spirit and scope of the invention as those skilled in the art will readily understand. Such modifications and variations are considered to be within the purview and scope of the invention and appended claims.

We claim:

1. A metal melting process wherein a metallurgical addition agent is added to the melt, in the form of aluminium-containing particles having on the particles coatings comprising at least one of the metals selected from the group consisting of nickel, cobalt and iron, said coatings encapsulating said particles sufficiently to prevent reaction of the aluminium-containing particles with air prior to addition of the agent to the melt.

2. An electroslag remelting process wherein a metallurgical addition agent is added to the slag pool in the form of coated aluminium-containing particles, the coating comprising at least one of the metals selected from the group consisting of nickel, cobalt and iron.

3. A process as claimed in claim 2 wherein the coated particles are coated aluminium powder.

4. A process as claimed in claim 2 wherein the coated particles are coated particles of an aluminium-based alloy.

5. A process as claimed in claim 4 wherein the aluminium-based alloy is selected from the group con- 6. A process as claimed in claim 2 wherein in excess of 20% by weight of the coated particles comprises nickel.

7. A process as claimed in claim 2 wherein the coated particles are in the size range 0.2 to 1.5mm.

8. A process as claimed in claim 2 wherein simultaneous additions of coated particles of at least one of calcium and magnesium are made, in which the coating is at least one of the metals selected from the group consisting of nickel, cobalt and iron.

9. A process as claimed in claim 2 wherein the coated particles are admixed with premixed metal powders of a desired composition and surround an electrode in rod form.

10. A process as claimed in claim 2 wherein the coated particles are admixed with premixed metal powders of a desired composition and surround an electrode in strip form.

11. A metallurgical addition agent comprising particles of an aluminium-lithium alloy having a coating of at least one of the metals selected from the group consisting of nickel, cobalt and iron.

12. A metallurgical addition agent as claimed in claim 11 wherein the alloy has the composition 5 to 45% lithium, by weight, balance aluminium and impurities.

13. A metallurgical addition agent as claimed in claim 12 wherein the alloy has the composition 16 24% lithium, by weight, balance aluminium and impurities.

14. A metallurgical addition agent as claimed in claim 11 wherein at least 20% by weight of the coated particles comprise nickel.

15. A metal melting process including the step of adding a metallurgical addition agent as claimed in claim 11 to a melt.

16. A.cast product when produced by a process as claimed in claim 2.

17. A cast product when produced by a process as claimed in claim 15. m 

1. A METAL MELTING PROCESS WHEREIN A METALLURGICAL ADDITION AGENT IS ADDED TO THE MELT, IN THE FORM OF ALUMINUM-CONTAINING PARTICLES HAVING ON THE PARTICLES COATINGS COMPRISING AT LEAST ONE OF THE METALS SELECTED FROM THE GROUP CONSISTING OF NICKEL, COBALT AND IRON, SAID COATINGS ENCAPSULATING SAID PARTICLES SUFFICIENTLY TO PREVENT REACTION OF THE ALUMINUM-CONTAINING PARTICLES WITH AIR PRIOR TO ADDITION OF THE AGENT TO THE MELT
 2. An electroslag remelting process wherein a metallurgical addition agent is added to the slag pool in the form of coated aluminium-containing particles, the coating comprising at least one of the metals selected from the group consisting of nickel, cobalt and iron.
 3. A process as claimeD in claim 2 wherein the coated particles are coated aluminium powder.
 4. A process as claimed in claim 2 wherein the coated particles are coated particles of an aluminium-based alloy.
 5. A process as claimed in claim 4 wherein the aluminium-based alloy is selected from the group consisting of aluminium-calcium, aluminium-magnesium and aluminium-lithium alloys.
 6. A process as claimed in claim 2 wherein in excess of 20% by weight of the coated particles comprises nickel.
 7. A process as claimed in claim 2 wherein the coated particles are in the size range 0.2 to 1.5mm.
 8. A process as claimed in claim 2 wherein simultaneous additions of coated particles of at least one of calcium and magnesium are made, in which the coating is at least one of the metals selected from the group consisting of nickel, cobalt and iron.
 9. A process as claimed in claim 2 wherein the coated particles are admixed with premixed metal powders of a desired composition and surround an electrode in rod form.
 10. A process as claimed in claim 2 wherein the coated particles are admixed with premixed metal powders of a desired composition and surround an electrode in strip form.
 11. A metallurgical addition agent comprising particles of an aluminium-lithium alloy having a coating of at least one of the metals selected from the group consisting of nickel, cobalt and iron.
 12. A metallurgical addition agent as claimed in claim 11 wherein the alloy has the composition 5 to 45% lithium, by weight, balance aluminium and impurities.
 13. A metallurgical addition agent as claimed in claim 12 wherein the alloy has the composition 16 - 24% lithium, by weight, balance aluminium and impurities.
 14. A metallurgical addition agent as claimed in claim 11 wherein at least 20% by weight of the coated particles comprise nickel.
 15. A metal melting process including the step of adding a metallurgical addition agent as claimed in claim 11 to a melt.
 16. A cast product when produced by a process as claimed in claim
 2. 17. A cast product when produced by a process as claimed in claim
 15. 